Optimization of injection-withdrawal schedules for underground gas storage in a multi-block depleted gas reservoir considering operation stability.

Underground gas storage (UGS) is an important facility to overcome the imbalance between natural gas supply and demand. In this paper, an optimization model of injection-withdrawal scheduling for UGS in a depleted gas reservoir is established to find the optimal operating state of the gas storage facility. Faults are widely developed in reservoir, which can divide a full reservoir into several pressure disconnected reservoir blocks (RB). Considering that the unbalanced pressure distribution of reservoir will significantly affect the stable operation of UGS, the optimization model aims to minimize the deviation degree of pressure between RBs under the condition of satisfying the gas injection-withdrawal requirements. The decision variables are the number of operating wells and the flow rate of a single well of each RB. A series of equality and inequality constraints are developed, including maximum inventory of RB, maximum pressure of RB and maximum flow rate of a single well. To verify the validity of the proposed method, the optimization model is applied to an actual UGS in a depleted gas reservoir in China. The GAMS modeling system and DICOPT solver are adopted to solve the optimization problem. The results show that the deviation degree of pressure between RBs of the optimized scheme is about 75% lower than that of the empirical scheme. In the empirical scheme, there is an extremely high-pressure RB with a maximum pressure of 43.98 MPa, which exceeds the pressure limit of 5.38 MPa. However, all RBs meet the pressure requirement in the optimized scheme. Overall, the optimized scheme can effectively reduce the deviation degree of pressure between RBs and avoid the occurrence of extremely high-pressure RB. [ABSTRACT FROM AUTHOR]